A non-uniform model for alternating current field measurement of fatigue cracks in metals

Abstract

The ACFM technique has been proved to be an extremely practical NDE method for crack detection and sizing. Its original mathematical model is based on a uniform interrogating surface current field. In this paper, the theoretical aspects of the ACFM technique are re-examined. The thin-skin theory of electromagnetic perturbation due to a surface-breaking crack has now been generalised to allow non-uniform interrogating current fields and has then been combined with the theory of electromagnetic induction in a half-space to produce a non-uniform ACFM model. More realistic simulations of many types of ACFM probes are obtained from the new theoretical model.